It is known to use quartz crucibles during crystallising of pure molten silicon by directional solidification and by crystal pulling from pure molten silicon, Quartz crucibles have, however, the drawback that quartz is wet by molten silicon, and solidified silicon will thereby affix to the walls in the quartz crucibles. Further, quartz and silicon have different coefficients of thermal expansion, resulting in that when molten silicon solidifies in a quartz crucible, thermal stress will be introduced in the quartz crucible which will destroy the crucible. Quartz crucibles can therefore only be used once.
From JP-59-62199 it is known a method for the production of silicon nitride crucibles for use in pulling silicon crystals. The crucible according to JP-59-62199 can be produced by forming silicon powder by cold pressing, whereafter the crucible is heated in an inert atmosphere in a first step and thereafter nitridation is carried out at a higher temperature in a second step. According to JP-59-62199 the produced crucibles have a density of 85% of the theoretical density for silicon nitride.
The crucibles according to JP-59-62199 have a good strength, but are wet by molten silicon to such an extent that the solidified silicon ingot sticks to the walls in the crucible. The ingot can thus not be removed from the crucible without destroying the crucible. The crucibles according to JP-59-62199 can thus only be used once when they are used for directional solidification of silicon. The same is true also when the crucibles according to JP-59-62199 are used for crystal pulling of silicon single crystals.